What is traumatic brain injury (TBI)?

Traumatic brain injury can be defined as an injury to the brain due to mechanical forces. Mechanical forces usually include falls, car accidents, accidental forces from another person or animal. It also includes sports-related brain injuries.

Are there different levels of TBI?

Yes. Usually brain injuries are categorised by severity levels into three groups:

mild

moderate

severe

The differences between these three groups are the duration of coma, or unconsciousness and the duration of post-traumatic amnesia, or loss of memory of the event of the injury.

How common was TBI previously estimated to be?

The previous estimates varied from 40-600 cases per 100,000 people. The variation in the estimates was largely due to differences in the methods of capturing traumatic brain injuries in the study populations.

What did your recent research suggest about the worldwide incidence of TBI?

Our research was the first in the world that used prospective, population-based methodology that captured both hospitalised and non-hospitalised cases of traumatic brain injuries across all ages and across all levels of severity of traumatic brain injuries, particularly mild traumatic brain injury. Our study found incidence rates that were six times higher than previous estimates.

We expect that differences in methodologies that we used compared to previous studies explain to a large extent the differences in the levels of incidences in our population compared to other populations. We expect similar incidence rates in other developed countries and if we approximate our estimates to the world population, we would expect about 50 to 60 million traumatic brain injuries happening every year - that means there are about 1-2 traumatic brain injuries per second.

What did your study involve?

Our study involved capturing hospitalised and non-hospitalised traumatic brain injury. We found that 35% of people who suffer a traumatic brain injury were never admitted to hospital. This is a big proportion.

Secondly, 95% of all traumatic brain injuries are mild, as opposed to 70-90% of previous estimates.

Did your research find any particular groups of people were most at risk of TBI?

Yes. The most affected group of people were men. They had 77% higher risk of sustaining brain injury compared to women.

Also, 70% of all brain injuries are happening in people younger than 35 years. This is also different from previous estimates that suggested up to 40% of brain injuries are happening in this age group.

The other quite important finding that was not consistently shown in previous research was that a very high proportion of brain injuries were caused by falls. Previously most research showed that car accidents were the most prevalent source of brain injury. Our study showed that falls accounted for 40% of all brain injuries and car accidents only account for 21% of all brain injuries.

Why do you think men and people under 35 years of age were most at risk of TBI?

We can only speculate on this. The most likely explanation is that these people are associated with more high injury risk activities. It is also known that men aged 20-35 years are more exposed to alcohol, sport activities etc.

Why do you think the results of your study differ so greatly from previous estimates?

The main reason is the difference in methodology. Our study was the most comprehensive. Previous research was largely confined to hospitalised cases and official statistics based on hospitalised cases or cases served in the community.

The most likely impact is two-fold. First, it will, and already did, attract attention to the problem. The problem of TBI is far greater than anybody anticipated before. Coupled with previous WHO estimates, it is predicted that TBI will be the third leading cause of disease burden in the world by 2020. Our research actually confirms these projections and estimates.

The second most important and desirable outcome is to stimulate more epidemiological research into TBI incidence and outcome. Our study showed clearly that there is an obvious lack of comparable population based research.

We also provided clear guidelines for conducting such population based research. This is important and was probably one of the reasons why there was no population based research before – because there was no methodology proved reliable for such research.

How do you think the incidence of TBI can be reduced or prevented?

That is a whole new area of research. Our study was not designed to address this question. But, looking at the mechanisms of TBI and analysing the mechanisms can inform preventative strategies. For example, falls in people under 35 years of age are a very important cause of TBI – especially in children under 5 years. That certainly gives the idea that maybe something should be done to prevent falls in this age group of the population.

Certainly more research needs to be done into the risk behaviours that lead to brain injury.

About Professor Valery Feigin

Professor Feigin is Professor and Director of the National Institute for Stroke and Applied Neurosciences, Faculty of Health and Environmental Sciences at the AUT University of Auckland.

He graduated in medicine from the Novosibirsk Medical University, Russia, and undertook advanced training in neurology and clinical epidemiology in Mayo Clinic, Rochester, MN, USA and Erasmus University, Rotterdam, The Netherlands.

Professor Feigin’s prime research interest is in the epidemiology, prevention and management of stroke and traumatic brain injury. He has published over 350 research articles in leading international and local medical journals (including The Lancet and The Lancet Neurology), and eleven stroke handbooks and twelve book chapters.

Professor Feigin is Editor-in-Chief of the journal Neuroepidemiology and a member of the Editorial Boards of 10 international medical journals. He currently leads the Stroke Experts Panel of the Global Burden of Disease Project that contributes data to the WHO regular reports distributed all over the world.

He is also a Director of the Board of Directors of the World Stroke Organization and a member of the Advisory Working Group on Stroke for the WHO ICD-11 version.

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